Medliorate

Improving medical students

MRSA: What Med Students Should Know

Posted by medliorator on December 5, 2007

by Alison Hayward, M.D.
SDN Staff Writer

MRSA rose to prominence last month when a CDC report published in JAMA estimated that nearly 19,000 people had died of MRSA infections in 2005. Compare that with AIDS, which killed about 17,000 in the same year,

 

Staphylococcus aureus is a bacterium that was discovered in 1880 in surgical abscesses. Staph has a talent for antibiotic resistance, and it became resistant to penicillin nearly immediately after penicillin was introduced in the 1940s. Methicillin is an antibiotic that was used to treat this penicillin-resistant staph, but as the bug continued to collect resistances, MRSA was born.

 

MRSA is a strain of staph that was identified in 1961. MRSA is by no means a new bacteria, it is only new to the public consciousness. Due to the mathematics of infectious disease, MRSA has exploded along an exponential curve and now represents the majority of all staph infections seen in ICUs and in the ED.

 

MRSA is potentially lethal, as is its parent, the pan-sensitive Staph aureus, often via bloodstream infections or bacteremia that leads to sepsis and ultimately to septic shock. However, MRSA is not deemed a superbug simply due to its resistance. It also has increased morbidity due to the accumulation of toxin genes via bacteriophages, such as Panton-Valentine leukocidin (PVL). A bacteriophage is basically a virus containing a snippet of DNA that can spread through a population of bacteria, similarly to the way a bacterial infection spreads through a human population. PVL is called a ‘leukocidin’ because it has the ability to burst white blood cells (leukocytes).

 

MRSA can be treated empirically with vancomycin, a “big gun” antibiotic. However, many may not be aware that MRSA is also often susceptible to such “small guns” as doxycycline or trimethoprim/sulfamethoxazole. As with any infectious disease, the best strategy is to start broad coverage antibiotics immediately with any suspicion of MRSA infection, and then to narrow coverage based on culture and sensitivity results. A CA-MRSA abscess, the most common manifestation that a normal, immunocompetent member of the community might face, can still be treated with a simple incision and drainage (I&D) of the wound. CDC recommendations suggest not adding antibiotic coverage unless the patient is immunocompromised, has severe local symptoms or signs of systemic infection, or does not respond to I&D. Antibiotic choices for outpatient treatment of MRSA skin infection include clindamycin and doxycycline.

  • Colonization with MRSA does not equal infection. Many people (an estimated 2 million in the U.S.) carry MRSA with no symptoms at all.
  • MRSA infection is treatable with proper antibiotics, and does not always require antibiotics.
  • Simple prevention strategies can greatly reduce the likelihood of a MRSA infection, particularly a severe one.

Community Acquired (CA)-MRSA and Hospital Acquired (HA)-MRSA have historically been significantly different bacteria. HA-MRSA strains tend to have accumulated resistance to more antibiotics, but CA-MRSA is actually more toxic. CA-MRSA can replicate more rapidly and is more often associated with PVL toxin, presumed to be a key factor in how CA-MRSA infections notoriously produce necrotic lesions such as abscesses or hemorrhagic pneumonia. New studies have shown that CA-MRSA can basically pulverize white cells, with or without PVL toxin, and that makes CA-MRSA hard for our bodies to defend against despite the fact that it is not resistant to as many antibiotics as its hospital-acquired cousin. There are several of these highly virulent strains of CA-MRSA that are now wreaking havoc in the community, the most famous of which is the USA300 strain.

MRSA: What Health Care Providers Should Know [Student Doctor Network]

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